Cooling and dust exhaustion plant for foundry sand

ABSTRACT

Cooling and dust exhaustion plant for foundry sand, comprising:  
     a substantially closed structure defining a cooling channel extending according to a longitudinal axis and with an inlet section for the sand to be treated and an outlet section for the treated sand,  
     a heat exchanger positioned inside the aforesaid structure and extending along the longitudinal axis of the cooling channel,  
     a cooling circuit to allow a flow of cooling fluid to circulate in the heat exchanger,  
     a fan positioned to send an air flow to an air chamber positioned under said heat exchanger,  
     a dust suction chamber positioned above said heat exchanger, and  
     a suction duct communicating with said suction chamber and associated with a filter unit,  
     in which the heat exchanger comprises a plurality of tubes which extend in a transverse direction in relation to said longitudinal axis.

[0001] The present invention relates in general to the field of foundries, and concerns a cooling and dust exhaustion plant for foundry sand.

[0002] Sand is used in foundries as refractory material suitable to create a shell which reproduces the internal and often the external cavities of the casting to be cast. For this purpose, the sand may be used without binders (for example in the process called “lost-foam”), or with chemical binders.

[0003] In the present description, and in the claims below, the term “sand” is used in the current meaning attributed to this term in foundry techniques, that is to indicate sand of any type and nature and particulate materials corresponding to sand, therefore with the exclusion of the finest grained material, currently called “dusts”.

[0004] The sand used in foundries is a material of a certain value and cost, and is often recycled. If the sand is dissolved and without binders, it is cooled and the dust is exhausted. If the sand contains binders a phase is required to eliminate these binders prior to the cooling and dust exhaustion phase. In any case, the process to recycle foundry sand always comprises a phase to cool the sand to a temperature in which it may be re-used and elimination of the dusts and fine grained components with dimensions below the minimum acceptable dimensions of the grains of sand.

[0005] A typical cooling and dust exhaustion plant for foundry sand comprises a substantially closed base structure defining a cooling channel which extends according to a horizontal longitudinal axis and at its ends has an inlet section for the sand to be treated and an outlet section for the treated sand. Typically, in cooling and dust exhaustion plants for foundry sand, the sand to be treated is fed into the plant at a temperature varying from 100 to 800° C. and is delivered at a temperature of about 20-50° C. The mass of sand is conveyed continuously from the inlet section towards the outlet section of the channel in the presence of an air flow directed from the bottom towards the top which generates a sort of fluid bed around the mass of sand. A tube nest heat exchanger is provided in the cooling channel, inside which a flow of cooling fluid, normally water, travels. The air flow forms a heat exchanging vehicle between the mass of sand and the tube nest of the heat exchanger. Moreover, the action of the air flow removes the dust from the mass of sand. These dusts are extracted by means of a suction and filtering system positioned over the cooling channel.

[0006] In known solutions, the tubes of the heat exchanger travel in a longitudinal direction for the entire length of the cooling channel. Therefore, the heat exchanger is substantially composed of a single block of considerable length. This block of tubes therefore has noteworthy dimensions and weights which are a source of problems when performing maintenance operations on the heat exchanger.

[0007] The present invention sets itself the object of providing a cooling and dust exhaustion plant for foundry sand which permits maintenance operations to be made simpler.

[0008] According to the present invention this object is attained by a cooling and dust exhaustion plant for foundry sand, comprising:

[0009] a substantially closed structure defining a cooling channel extending according to a longitudinal axis and which has an inlet section for the sand to be treated and an outlet section for the treated sand,

[0010] a tube nest heat exchanger positioned inside said structure and extending along the longitudinal axis of the cooling channel,

[0011] a cooling circuit to allow a flow of cooling fluid to circulate in the heat exchanger,

[0012] a fan positioned to send an air flow to an air chamber extending in the aforesaid cooling chamber under said heat exchanger,

[0013] a dust suction chamber extending in the cooling channel above said heat exchanger,

[0014] a suction duct communicating with said suction chamber and associated with a filter unit,

[0015] in which the tubes of the heat exchanger extend in a transverse direction in relation to said longitudinal axis.

[0016] Preferably, the heat exchanger comprises a plurality of modules, each of which is movable in relation to the base structure in the aforesaid transverse direction between an inserted position and an extracted position.

[0017] The present invention shall now be described in greater detail with reference to the accompanying drawings, provided purely as a non-limiting example, in which:

[0018]FIG. 1 is a base diagram showing a plant according to the present invention,

[0019]FIG. 2 is a schematic section according to the line II-II in FIG. 1,

[0020]FIGS. 3 and 4 are schematic sections corresponding to FIG. 2 and showing the positions in which a module of the heat exchanger is in the partially and completely extracted position,

[0021]FIG. 5 is a side view of a module of the heat exchanger, and

[0022]FIG. 6 is a section according to the line VI-VI in FIG. 5.

[0023] With reference to FIG. 1, the reference number 10 indicates as a whole a cooling and dust exhaustion plant for foundry sand. The plant 10 comprises a base structure 12 substantially closed with an elongated form in a horizontal longitudinal direction X. The base structure 12 is obtained by metalworking operations and rests on the ground by means of a sturdy base schematically indicated with 14. In practical embodiments, the base structure 12 may have a length in the longitudinal direction X exceeding ten metres. Positioned at opposite ends of the base structure 12 are an inlet section 16 for the sand to be treated and an outlet section 18 for the treated sand. The inlet and outlet sections 16, 18 are represented schematically as ducts communicating with the internal volume of the base structure 12. In the practical embodiments, it is intended that the inlet and outlet sections will be designed to facilitate the flow of the quantity of sand that the plant is destined to treat, which may be in the range of 10 to 100 tonnes per hour.

[0024] The base structure 12 defines a longitudinal cooling channel 20 to contain a mass of sand to be treated indicated with S which during use moves continuously from the inlet section 16 towards the outlet section 18.

[0025] A tube nest heat exchanger 22 extends inside the base structure 12. The heat exchanger 22 extends along the longitudinal axis X for the entire length or for a substantial part of the length of the cooling channel 20. The tube nest heat exchanger 22 is connected to a cooling circuit 24 positioned so that a flow of cooling fluid, typically water, is circulated in the heat exchanger 22. The cooling circuit 24 comprises a circulation pump 26 and a cooling unit 28 composed for example of an evaporation tower.

[0026] Defined inside the base structure 12 are an air chamber 30 which extends below the heat exchanger 22 and a suction chamber 32 for dusts which extends above the heat exchanger 22 and above the mass S of sand to be treated. The air chamber 30 is delimited at the top by a plate 34 which supports the mass of sand S. The plate 34 is provided with openings or nozzles schematically indicated with 36 which permit air to flow from the bottom towards the top and which prevent sand from falling from the top towards the bottom. The air chamber 30 is connected to a fan 38 operated by an electric motor 40. The dust suction chamber 32 communicates with a suction duct 42 associated with a filter unit 44 and with an exhaust fan 46. Positioned downstream of the exhaust fan 46 is a flue 48 for releasing the air flow purified from the dusts into the atmosphere.

[0027] During operation, the mass of sand S moves continuously along the cooling channel from the inlet section 16 towards the outlet section. The fan 38 generates pressure in the air chamber 30 which maintains an air flow that moves from the bottom towards the top through the mass of sand S. The air flow increases the heat exchanging efficiency between the sand and the heat exchanger 22 and removes dusts and impurities present in the mass of sand S. The dusts and impurities are collected in the suction chamber 32 and are extracted through the suction duct 42. The filter unit 44 separates the dusts from the air flow and the air flow purified from dusts and impurities is finally released into the atmosphere. As the mass of sand S travels through the cooling duct 20, the temperature of the sand decreases progressively. For example, the feed temperature initially in the range of 100 to 800° C. decreases in the outlet section to about 20-50° C. At the same time, the action of the air flow removes dust from the mass of sand S. Upon delivery from the cooling channel 20, the sand treated in this manner is conveyed to the plant in which it is used.

[0028] With reference to FIGS. 2 to 5, according to the present invention the heat exchanger 22 comprises a plurality of tubes 50 which extend in a transverse direction in relation to the longitudinal direction X. The heat exchanger 22 is preferably divided into a series of modules 52 separate from one another and placed side by side in the longitudinal direction X. Each module has a series of tubes 50 which extends for the entire width of the cooling channel 20. Each module preferably includes a pair of manifolds 54, 56 for the feed and delivery of the flow of cooling fluid. The tubes 50 are connected parallel to one another between the manifolds 54, 56. In the embodiment shown in the figures, the two manifolds 54, 56 extend from opposite parts in relation to the base structure 12.

[0029] Each module 52 is fixed in a removable manner to the base structure 12 and may be extracted individually from the base structure 12 with a movement in a transverse direction in relation to the longitudinal axis X. FIGS. 3 and 4 show the position partly extracted and completely extracted of a module 52, respectively. A movable supporting structure 58 may be provided to support the module 52 which each time is in the extracted position. FIGS. 5 and 6 show that each module is provided with front plates 60 provided with holes 62 which are used for fixing with screws to the side walls 64 (FIGS. 2-4) of the base structure 12. After removing the screws which connect a module 52 to the base structure 12, this module may be extracted by applying force in the direction indicated by the arrows 66 in FIGS. 2 to 4. During the extraction movement, the module 52 is supported by the supporting structure 58. When the module 52 has been completely extracted (FIG. 4) it may be raised, for example using a bridge crane.

[0030] The heat exchanger 22 must be disassembled periodically to perform maintenance operations. For example, it is necessary to periodically remove the limestone that deposits in the tubes or bacterial formations that may form inside the tubes.

[0031] In traditional solutions in which the tubes of the heat exchanger extend longitudinally for the entire length of the cooling channel, the operation to disassemble the heat exchanger to perform the aforesaid maintenance operations is extremely time-consuming and difficult.

[0032] Thanks to the transverse position of the tubes 50 according to the present invention, it is possible to divide the heat exchanger into a series of individual modules which may be disassembled separately in a much simpler and faster manner than is possible in traditional type plants. The flow of cooling fluid may be made to pass in series through each module 52 or may be divided in parallel among all the modules. As a further alternative, it is possible to form two or more heat exchange units connected in parallel to the circuit 24 and in which each unit comprises two or more modules connected in series with one another. Therefore, in comparison with a traditional solution with longitudinal tubes it is possible to obtain distribution of temperature along the heat exchanger 22 which allows the heat exchange efficiency to be improved.

[0033] Naturally, without prejudice to the principle of the finding, the constructional details and embodiments may vary widely in relation to what is described and illustrated herein purely as an example, without however departing from the scope of the present invention as defined in the accompanying claims. 

1. Cooling and dust exhaustion plant for foundry sand, comprising: a substantially closed structure defining a cooling channel extending according to a longitudinal axis and which has an inlet section for the sand to be treated and an outlet section for the treated sand, a heat exchanger positioned inside the aforesaid structure and extending along the longitudinal axis of the cooling channel, a cooling circuit to allow a flow of cooling fluid to circulate in the heat exchanger, a fan positioned to send an air flow to an air chamber positioned under said heat exchanger, a dust suction chamber positioned above said heat exchanger, and a suction duct communicating with said suction chamber and associated with a filter unit, in which the heat exchanger comprises a plurality of tubes which extend in a transverse direction in relation to said longitudinal axis.
 2. Plant according to claim 1, in which the heat exchanger comprises a plurality of modules, each of which is movable in relation to the base structure in the aforesaid transverse direction between an inserted position and an extracted position.
 3. Plant according to claim 2, in which each module comprises an inlet manifold and an outlet manifold of the flow of cooling fluid which, in the aforesaid inserted position of the module, extend from opposite parts of said base structure.
 4. Plant according to claim 2, in which each of said modules is fixed to the base structure so as to be disassembled separately from the other modules.
 5. Plant according to claim 4, in which each module is provided with front plates for fixing to the side walls of the base structure.
 6. Plant according to claim 2, in which at least part of said modules are connected in series with one another with reference to the direction of circulation of the flow of cooling fluid.
 7. Plant according to claim 2, in which at least part of said modules are connected in parallel with one another with reference to the direction of circulation of the flow of cooling fluid. 